Most modern aircraft and spacecraft are manufactured using composite materials with carbon fibres. There are several techniques for manufacturing composite materials, like Resin Transfer Moulding (RTM), Vacuum Assisted Resin Transfer Moulding (VARTM), Resin Infusion Moulding (RIM), Fiber Placement (FP), Automated Fiber Placement (AFP) or Automatic Tape Lying (ATL). All these techniques are well known in the state of the art.
Preimpregnated materials (“prepregs”) are used in some of these techniques. When manufacturing prepreg materials sometimes defects are also created, so defective areas must be detected and registered. Prepreg manufacturers include a reference of defective areas associated to each prepreg roll. These defective areas can be controlled and scrapped when laying up using an encoder; an encoder is a device which measures the length of each prepreg material roll as it is being laid up. The prepreg manufacturer includes a defective areas list with each roll, so through the encoders' use it is possible to detect the proximity of a defective area. However, sometimes encoders are imprecise due to the fact that prepreg rolls may slip or encoders may reset; therefore, encoders' information may be wrong and some potential defective areas may be laid up on the part.
Current automatic tape laying machines include laser defect detection systems based on shade contrast. Nevertheless, the fine calibration of these defect detection systems is hardly achieved due to reflections produced by the incident light against the resin of the prepeg material. The system generates continuous false alarm situations because of these reflections. That is the reason why they are not accurate enough and are usually turned off.
This invention presents a system to overcome the mentioned drawbacks, marking failures in prepreg rolls. The object of the invention is to include transversal cross lines in the boundary of a defective area in a prepreg material. These transversal lines are marked with a non pollutant material having a chemical composition that do not contaminate the prepreg material; therefore, the marked lines mean no change of the technical features of the final product.
These marked lines allow detecting defective area in the prepreg material, avoiding their use in the parts that are going to be manufactured. The prepreg rolls having defective areas are cut and scrapped before the prepreg material is laid up with the ATL machine (or any other machine used during the manufacturing process). Therefore, a cost reduction is achieved due to the fact that manufactured parts do not include those defective areas, and the parts are not rejected when passing quality control inspections.
The state of the art shows different devices and procedures for manufacturing and supplying prepreg materials. Document WO 2008/120023 A1 discloses a method and apparatus for making thermoplastic prepregs with specific fiber orientation. Document JP 2005246631 A reveals a method for detecting different kinds of prepreg materials and apparatus thereof. However, no evidence about a procedure to recognize defective areas in prepreg materials according to the present invention has been found.